This invention relates to a hetero junction semi-conductor device which has at least one inter-semiconductor hetero junction.
2. Description of the Prior Art.
Heretofore, there have been proposed a variety of hetero junction semiconductor devices which have at least one inter-semiconductor hetero junction. Typical hetero junction semiconductor devices are as follows: a p-n or n-p type photo diode having one p-n hetero junction, an iso-type (n-n or p-p type) photo diode having one n-n or p-p hetero junction, a p-n-p or n-p-n type photo transistor having two p-n hetero junctions, a p-i-n or n-i-p type photo diode having one p-i hetero junction and one n-i hetero junction, an n-p-n-p or p-n-p-n type photo cell having three p-n hetero junctions, a p-i-i-n or n-i-i-p type photo cell having one p-i hetero junction, one i-i hetero junction and one n-i hetero junction, etc.
These hetero junction semiconductor devices are of the type that make effective use of a difference in height between a barrier against electrons injected from one of two semiconductor regions into the other across the hetero junction defined there between and a barrier against holes injected from the latter to the former.
The conventional hetero junction semiconductor devices are all made of a single crystal semiconductor, so that each hetero junction is formed abruptly between two single-crystal semiconductor regions having different energy gaps. And, since there is a difference in lattice constant between the two single-crystal semiconductor regions, dangling bonds are formed locally at the position of each hetero junction, and accordingly interface states or defects are present locally at the position of each hetero junction, resulting in an energy and band structure that has, at the position of each hetero junction, an energy spike or notch extending towards either one of a valence band and a conduction band.
Accordingly, in the prior art hetero junction semiconductor devices, during operation electrons or holes to be injected from one of the two semeconductor regions into the other across the hetero junction are partly absorbed by the interface states or defects appearing at the position of the hetero junction, and migration of electrons or holes from one of the two semiconductor regions to the other across the hetero junction is similarly limited by the energy spike or notch at the position of the hetero junction; therefore, the conventional hetero junction semiconductor devices have the defect that they cannot operate on large currents.